We asked to what extent hypoxia would modify the huddling behaviour of
young rats during cold exposure. Sets of five animals (postnatal age
9 +/- 1 days) were placed at predetermined positions in a chamber main
tained at similar to 33 degrees C (warm) or similar to 15 degrees C (c
old), in normoxia or hypoxia (10% inspired O-2), and their movements m
onitored for 30 min by a video camera. The surface areas (SA) of each
individual pup (SAi) and of the whole set of pups (SAset) was measured
every 5 min. In warm, the rats spread out, and both SAi and SAset wer
e the greatest, whether in normoxia or hypoxia. In hypoxia, the total
travelled distance (TTD) was much greater than in normoxia. In cold, d
uring normoxia, SAi and SAset were decreased because of postural chang
es and huddling, and body temperature, measured at the end of the expo
sure, was also decreased. In hypoxic-cold, compared to normoxic-cold,
fewer pups were in contact with one another, SAi and SAset did not dec
rease and the drop in body temperature was larger. Differently from hy
poxia, hypercapnia (5% CO2) did not modify the responses observed duri
ng breathing air, whether in warm or cold conditions. We conclude that
hypoxia, in addition to inhibiting shivering and non-shivering thermo
genesis, can also limit behavioural thermogenesis, with the effect of
further lowering body temperature. (C) 1998 Elsevier Science B.V. All
rights reserved.